The present invention relates to ceramic pin heating elements, and in particular, to a ceramic pin heating element for an internal combustion engine, the pin heating element having integrated connector contacts.
Connection of ceramic pin heating elements having exterior heating element shafts in a metal housing with simultaneous sealing from the combustion chamber is complex. The installation position causes contact between the heating element shafts having different polarity and the grounded housing. Therefore, to avoid short circuits, one of the two heating element shafts must be electrically insulated from the housing in the area of the seal seat. Also, the other heating element shaft, having opposite polarity, must be electrically insulated from the connector bolt. The application of electrical insulation layers is currently implemented through separate vitrification steps or through application, for example by printing, and burning-in of electrically insulating layers. To avoid one-sided mechanical stresses of the installed pin heating element due to the applied insulation layers, the corresponding open connector shaft is also provided with a layer of the same thickness but with electrical conductive properties, since there might otherwise be a danger of breakage of the ceramic pin heating element in the area of the seal seat. Another possibility is for the ceramic pin heating element to be fully insulated from the housing through application of a coating. As with a potential-free A-probe, contact is made through a divided terminal bolt.
The present invention provides a method for making a ceramic pin heating element having exterior conductors and integrated electrical connection surfaces. The method comprises injection molding a first body from a first injection-moldable ceramic composite compound having a first electrical resistance; injection molding a second injection-moldable ceramic composite compound having a second electrical resistance about the first body so as to form a compound body; and sintering the compound body.
The present invention also provides a ceramic pin heating element comprising a first body injection molded from a first injection-moldable ceramic composite compound, the first body having a first electrical resistance, and a second body injection molded from a second injection-moldable ceramic composite compound, the second body having a second electrical resistance. The first body and second body form a compound body, the compound body being sintered after injection molding of the first body and the second body.
A ceramic pin heating element according to an embodiment of the present invention has exterior heating conductors based on Si3N4/MSi2, where M is at least one of Mo, Nb, Ti and W, and has integrated electrical connection surfaces using multiple-component injection-molding technology.
An advantage of the method and heating element of the present invention is direct shaping of the pin heating element without additional steps for protecting (insulating) the element so as to prevent the exterior, complementary heating conductors from contacting the housing and/or terminal bolts. Another advantage according to the present invention is minimization of the danger of breakage of the pins at the mounting location and/or at the seal seat through variations in the thickness of contact and/or insulation coatings.